Hydraulic feed for machine tools



A. A. ERICSON HYDRAULIC FEED FOR MACHINE TOOLS lFeb. 26, 1952 3 Sheets-Sheet l Filed Feb. 10 1945 R N ww e mi O 0 E T 5 .v N E N fc R R E H o wv VE T 5 m fm M A o. \1 m\\ W .W E Y QQ\ M. f. B M Qu A #Wv Q` Feb. 26, 1952 A. A. ERlcsoN HYDRAULIC FEED EOE MACHINE TooLs 3 Sheets-Sheet 2 Filed Feb. lO, 1945 INVENTOR M55/PTA. T6/(50N B Y 477W/ Feb. 26, 1952 A. A. ERlcsoN 2,587,449

HYDRAULIC FEED EOE MACHINE TOOLS Filed Feb. 1o, 1945 s sheets-sheet 5 INVENTOR /M 55e?- A, :CQ/(50N 477m, M, @am -f ATTORNEYS Patented Feb. 26, 1952 UNITED STATES PATENT OFFICE 2,587,449 HYDRAULIC FEED FOR MACHINE TOOLS Application February 10, 1945, Serial No. 577,278

(ci. fio-51) 14 Claims. 1

This invention relates to hydraulic drives for machine tools, and particularly to drives controlling the relative movement of the tool and work so as to control not only the rate of feed, but also to prevent overfeed or overrun of the tool or work in the direction of feed. The invention is also particularly applicable to machine tools in which there is a cutting stroke in both forward and reverse directions of the travel of the parts.

The utility and advantages of the invention are especially apparent in connection with milling machines, and the invention will be described as applied to the operation of such machines. It will be understood, however, that some or all of the features of the invention may be used in the driving and control of other types of machine tools.

In considering the application of the invention to milling, and like machines, it will be apparent that it is frequently desirable to move the carriage of the machine (or the tool in case the feed is accomplished by movement of the tool) so as to bring about feed of the work with respect to the cutter, iirst in one direction and then in the opposite direction, so that there is no idle stroke. Such reversible feed requires full control over the movements of the carriage in both directions, and the present invention provides instrumentalities by which this may be accomplished. Furthermore, in milling operations there are two distinct conditions to be met with depending upon whether the work is moved in a direction in which its movement is opposed by the rotary cutting action of the tool (standard milling) or whether the rotary action of the tool produces forces acting in the same direction as the feed of the work (climb milling). In the case of climb milling, the rotation of the cutter tends to cause the carriage and work to move too fast and it is very important to properly control the feed so as absolutely to prevent the overfeed or too rapid movement of the carriage. In the event of such overfeed the tendency is for the work to be wedged under the cutter with probable breakage of the cutter, bending of the arbor, or other serious injury. The present invention eliminates such overfeed and therefore is particularly applicable to climb milling.

Features of the invention are applicable to securing a uniform feed, and proper control of feed in the performance of machining operations of various kinds, and in the different types of machine tools, whether operating in one direction only or reversible.

. vvIn vthe .accompanying drawings one embodi- Cil 2 bent of the invention has been shown as applied to a milling machine. The invention may however be embodied in other constructions, and applied to various devices in which a feed and control of the character described is desirable.

In the drawings:

Figure 1 is a diagrammatic perspective'view of the illustrative embodiment of the invention showing the control valve set to feed the carriage from left to right;

Figure 2 is a similar view with the valve set to feed the carriage from right to left; and

Figure 3 is a view partly in front elevation and partly in vertical section showing one of the automatic pressure regulators used in the system.

Referring to the drawings in detail, Ill is the carriage of a milling machine upon which is secured a work piece indicated at I2. I4 is a milling cutter having a plurality of teeth I6, the cutter being mounted on the arbor I8 rotated in any suitable manner as is well known in milling machines. In the present example the arbor of the milling cutter is assumed to be mounted to rotate in a stationary support indicated at 20, while the carriage is moved. If desired the carriage could be stationary and the milling cutter arbor carried by a movable support or both carriage and cutter support could be moved. As shown, the carriage III is arranged to be reciprocated by means of a piston rod 22 carrying a piston 24 working in a hydraulic cylinder 26. The cylinder, piston and piston rod may be collectively referred to as the actuator. Any other form of hydraulically operated actuator may be used.

The ends of the cylinder are connected with pipe lines 30 and 32 which run to a control valve 34 which may be of any suitable type and which acts as a shut-off and reversing valve. The control valve 34, however, differs from known control valves in that it also establishes connection with the pilot control of an automatic pressure regulator as will be described below. In one position of the valve the liquid under pressure is directed to one end of the cylinder through one of the pipes 30 or 32 as the case may be. These pipes therefore respectively act as power lines or exhaust or relief lines depending upon the position of the control valve. The control valve shown for purposes of illustration comprises a cylindrical casing 36 having a rotary plug 38 therein. As illustrated, the plug is provided with two Y-shaped passages, one indicated at 40 near the right hand end of the plug, and the other at 42 (shown in dotted lines) near the left hand end 3 of the plug. The casing 36 has suitable ports with which the passages in the plug are adapted to be brought into registration by partial rotation of the plug.

Figure 1 vshows the plug turned to a position to supply liquid to the left hand end of the actuator cylinder so as to produce movement of the milling machine carriage towards the right. Figure 2 shows the plug 38 moved to a reverse position so as to cause the carriage to travel towards the left. Liquid under pressure is supplied to. the control valve through a power line 50, which. leads to a T 52 having a branch 54 connected to a port 5S in the left handeudof the valye casing 36 with which one of the. branches of thepassage 42 is adapted to register in one position of the plug 38. The power line. is alsoV connected in the provision of automatic regulating means for regulating the pressure of liquid passing through the power line to the actuator and for regulating the discharge from the actuator. In the construction shown regulation of power line pressure is accomplished by means of an automatic regulator or pressure controlled valve indicated generally at I0, and one commercial form of Which is shown in Fig. 3. This comprises a throttle valve ||2 in the power line which is actuated in y any suitable manner, preferably by some external source of power.

by pipe 58 extending from the T 52 to a port'" in the right hand end of the casing 36thisl port4 60 being adapted to register with a branch of the passage 40. An exlflaustY or return line 62 is provided which is connected,-by means of a pipe 64 to a T 66, one branch of which is connect-ed to a port 68 near the righthand. end of the` casing 36 and adapted to be, brought into registration with a branch of the passagektl in the plug. The return line T 60y` is alsoconnected through a loop 'l0 with a port, '|2 in the left hand end of thel casing 36. Suchportisadapted to be brought into registration with a branchof the passage 42.

Figure 1 shows the, plug,n valve turned so that the power passes fromthepower line 50 through the pipe loop 58, por-t,v 60, plug passage 40 and pipe 3,0 to the left handV-.end of the actuator cylinder 26, thus moving the carriage4v I0 to the right. At this time the right hand endl 0f, the cylinder is relieved of liquid through pipe 32, pipe 80, port 82 in casing 36, plug passage` 42,l port '|2, pipe loop 10, pipe 64and return pipe02.

Figure 2 shows thecontrol valve reversed so thatv power from the power line isdirectedgto the right hand endl of the actuator cylinder through pipe 80 and p ipe 32.I The liquid is discharged from the left handend of the cylinderv through pipe 30 and the appropriate passages and ports inthev control valve to pipe 64and return line 6.2.

Power mayl be supplied for actuating the machine toolA feed from any suitable` source, such for instanceas by means of the system of supply described in my application for patent, Serial No. 567,437, filed. December 9, 1944 (now Patent 2,526,646,l issued Oct. 24 1950). For purposes of illustration I have indicated diagrammatically a source of fluid supply comprising a pump 9U drawing actuating fluid from a reservoir 92. Connected with the power line at all times by means of a pipe 94 is an accumulator 96 which has an air space 98 at its upper end in which air is,

trapped by the liquid in the system.` Leading from the air space 98 is an air pipe |00.the purpose of which will be described below. Also con: nected with the discharge from the pump is a relief valve |02, any overflow from which is discharged through a pipe |04 to the reservoir. This permits the pump to run steadily and provide a continuous supply of liquid under pressure,

any liquid not used being returned to the reservoir through the relief valve |02. The setting of the relief valve determines the maximum pres.- sure which may be supplied. The presence of the accumulator is important, its function inY cushioning the operations of the tool being setr forth and claimed in my application for patent Serial No. 567,438, led December 9, 1944.

An important feature of this invention-consists;

The throttle valve may be of any suitable form such as a needle valve or percentage pistonvalvej In the construction shown, the. valve |,IL2 actuated through the stem ||4 which is urgedv in a, direction to open the valve by a spring ||5 and is moved in a direction to close the valve by means of a diaphragm IIB which is vsuppliedwith pressure from any suitable source such as the shop air lifne IIB. The air pressure from this line is controlled by a pilot valve |20 which is actuated ,avvpressure responsivey element which in the. presentl instance is shown as a Bourdon tube` |22. When the Bourdon tube is actuated by variations. in pressure applied thereto, the valve |20 is operated, so asto vary the action of the air pressure upon. thediaphragm ||6 and thereby control the degree'. of opening of, the throttle valve H2, thus. regulating the pressure in the power line which passes from the latter through the control val-ve 34 to one or the other of the ends of` the actuating` cylinder, depending uponthe setting of the control valve at any particular time. The pilot valve |20l includes a head |20a which is adaptedl at times to seat upon a lower valve seat, |201). or an upper valve seat |20c. When the valve head |20a is off its lower seat |20b, the air from the conduit ||8 will act upon the upper surface of the diaphragm H6,y and when the valve head is off. its upper seat |20c. the air trapped inthe pipe leading tothe diaphragm I6 will escape to the atmospherethrough a vent |2011. The pressure responsive element or Bourdon tube |22 isv actuated by means-of pressure supplied through pipe |30 which is at all times connected. to the power line and actuator through the control valve-34. In the particular construction illustrated in Fig. 3, increased pressure on the` Bourdon tube increases the openingl of thevalve |20 to supply air to the space above the diaphragm ||6 for reducing the opening of the valve H2, andvice. versa. In order'to establish connection. from the power line to the line |30, the casing 36 is provided Vwith anextra port near each end, the port at the left hand end adapted` to register with. theplug passage 42 being designated |40, and the corresponding port at the righthand end. of the casing being designated |42. With the construction shown itwill be seen that the pipe |30is always in connectionwith the power line` through one or the other of` theseports, so thatthe Bourdon tube |22 is responsive to the` pressure in the power linev for both directionsof feed of the carriage. The regulator ||0 is provided with a manually-adjustable control which isV actuated by setting the hand |44 on. the dial |46 inwell known manner.

The operation of the regulator |50 is as folV lows: The hand- |44 is set so as to provide for themaintenance of the pressure necessary tosecure the desired tool loading or thickness of chip. This loading isl selected by. considerations ofthe nature of thework andv cut, hardness of the material, character of the tool, etc., as3is1well. understood. Thev primary functionl of the; automatic regulator is to" compensate for changes which may occur in the conditions of operation of the tool. For example, if the nature of the work is such that the depth of the cut decreases suddenly or considerably, so that the load opposing the feed of the work is substantially decreased, and the resistance to movement of the actuator decreased, there will be a tendency for the liquid to surge more rapidly into the actuator cylinder which will result in a momentary decrease in the pressure in the power line. This will result in the decrease in pressure in the line |30 leading to the Bourdon tube |22 in the regulator. Such decrease in pressure in the Bourdon tube permits the tube to curl inwardly which releases pressure on the stem of valve |20 thus permitting valve head |20a to move toward its lower, closed position with respect to ow of air through conduit |I8, see Figure 3. Such lowering movement of valve head |20a permits air trapped above diaphragm ||6 to escape to atmosphere through port |20d, which permits valve l2 to move to its open position under the urgency of spring acting on diaphragm H8. This increases the ow of liquid in the power line and resultant pressure in the actuator, and thereby compensates for the tendency of the actuator to move at a slow rate upon load removal. On the other hand, if the tool strikes a hard spot or encounters a heavy cut, then the resistance to movement of the carriage and actuator is increased. This tends to slow down the feed, and the pressure in the actuator builds up in the effort to overcome the increased resistance. This results in an increase in pressure in the pipe |30 and Bourdon tube. Such increase in pressure causes the valve |20 to partially or wholly open, thus increasing the air pressure acting on the diaphragm ||6. This forces the stem ||4 down to decrease the opening of the valve ||2, thereby decreasing the pressure of liquid acting inthe actuator to compensate for the increased resistance to movement of the carriage. 'Ihus the liquid supplied to the actuator is varied in accordance with the resistance to be overcome.

The construction described above provides means for controlling the application of power, that is liquid under pressure to that end of the cylinder which for the time being is acting as the power end. Obviously upon reversal of the control valve, similar control of the liquid to the other end of the cylinder will be provided. To properly control the movements of the tool or carriage, however, it is in many cases necessary to control the discharge of liquid or relief of pressure from the discharge side of the cylinder as well as to control the power ow leading to the power side. This control may be referred .to for convenience as the discharge control as opposed to the power control. In the construction shown the discharge control is accomplished as follows: An automatic regulator or valve |50 is provided for controlling the flow in the return line, this regulator being similar to the regulator ||0 described above. Like the former it comprises a valve |52 in the return line actuated from a diaphragm |58 which is actuated by means of air pressure from the shop air line ||8. The regulator contains a Bourdon tube |58 which actuates an air valve. In this instance the pressure which actuates the Bourdon tube is air pressure instead of liquid pressure, and such air pressure is that produced in the air space 98 in the top of the accumulator 96 which passes to the Bourdon tube through the pipe |00. The control of the return '6 line bythev regulator |50 is' independent of the setting oi the control valve 34, so that it acts upon the return or discharge from the actuator irrespective of the direction of feed produced by the latter.

The operation of controlling the return line by means of the regulator |50 is as follows: Assuming there .is a sudden decrease in the resistance to movement of the carriage I0, caused for instance by a decrease in the depth of cut due to the shape of the work piece, there is a surge of liquid in the power side of the actuator cylinder due to the decrease in resistance and tendency for more rapid movement of the carriage. This surge of liquid decreases the pressure in the power line as already described. It also tends to force more liquid through the return line from the other side of the cylinder. The decrease in pressure in the power line, however, results in an immediate movement of liquid from the accumulator 98 to make up for the surge of liquid through the power line to the actuator cylinder. This lowering of the liquid level in the accumulator causes decrease in pressure in the air space 98 on top of the liquid in the ac cumulator and thereby results in lowering of the pressure in the pipe |00 and Bourbon tube |58. This results in decreasing the opening of the pilot valve of regulator |50 thereby lowering the air pressure above the diaphragm |55 and increasing the opening of the valve |52 thereby decreasing the throttling of the ilow of liquid from the actuator through the return line and permitting more rapid movement of the actuator piston and carriage. On the other hand, if the feed of the carriage encounters an increase in resistance, then the pressure in the power line increases, as already described. This results in an increase in pressure in the accumulator, and an increase in air pressure in the air space 98, pipe |00 and Bourbon tube |58. Such increase tends to close the valve |52, increasing the resistance to flow of the liquid in the return line. This results in increasing the back pressure in the actuator cylinder and thereby prevents the rising pressure in the power side of the cylinder from applying its full power in driving the actuator so as to overcome tendency to increase the pressure of the work against the tool beyond the desired loading in response to increased resistance met with by the tool, and thereby enable the feed of the work to be kept up as near to the desired maximum pressure as possible. This maintains the tool load and chip thickness substantially uniform.

In order to prevent the pressure in the power line and power side of the actuator cylinder from ever building up a dangerous value, it is desirable to provide relief valves between the main control valve and the actuator cylinder, one such valve being providedv for each end of thev cylinder so that they can operate alternately depending upon which side of the cylinder is for the time being acting as the power side. Such relief valves are shown at and |82. The valve |80 is connected to the line 35 by branch |84 and in the case of the pressure rising to a point higher than that for which the relief valve is set then the surplus liquid is discharged through the pipe |88 to the return line. A gauge |88 may be provided to show the pressure in line 30. The relief valve |82 is connected to the line 32 by branch |90, a gauge |92 being provided to show pressure. Any liquid passing relief Valve |82 goes into thereturn-line vthrough a pipe |95.

' It is often desirable to provide a fast feed for the carriage except during the time when the Work is actually passing under the tool. This may be accomplished in the construction of the' pres# ent invention by providing valve means cutting oi the air pressure Which actuates the diaphragms H6 and |56 during the times when rapid movement of the carriage is desired. If this air pressure is cut off then the springs in the pressure regulators fully open the valves H2 and |52 thereby permitting application of the full hydraulic pressure available to'inove the actuator rapidly. Means are' preferably provided for automatically turning on the air pressure so as to control the feed just prior to the'V engage ment of the tool with the Work, ln the construc# tion shown a valve' 200 is provided in the air pressure line which is normally closed by a spring (not shown) thus cutting off the air to the pressure regulators. The valve: 206' is arranged to be opened by a cam 262 mounted on a shaft 2te Which carries a trip rocker 265i The latter is arranged to be tripped by a pin 258Y mounted on a slide 2|!) adjustably secured to the carriage. The slide is adjusted so that the pin 2138 will' engage the trip lever and rock it sor as to rotate the cam 202 and open the valve 200 therebyV turning on the air just at the time that the Work piece engages the' tool. On the return stroke of the carriage after the Workpiece has passed the tool the trip rocker Will be tripped in the opposite direction thereby cutting oi the air and permitting the carriage to speed up; Gbviously any suitable arrangement of tripping or control devices for accomplishing the desired cycle of operations may be utilized.

From the forgoing descriptionof one particular example of the invention it'will beA seen that feed control means are provided' for a machine tool such as a milling machine'orv other tool in which similar conditions obtain, in which the relative feed of the work and tool are undercom'plet'e conf- A trol in both directions of feed and very quick acte ing means for regulating and preventing overfeed are provided which will effectivelyprevent movement of the carriage# at a fasterra'te tha-n the permissible rate of cuttingofthe tooli operation and high quality of work. At the'fsame time the control of the'apparatus is such that the' tool may be fed intoV the Work` at the highest possible speed compatible with proper-operation,

so that maxium output can be' obtained. Owing` to the sensitiveness and eiciency of theregulation, it issafe to' usea higher rate of'fee'd'thanI could be successfully employed'ifthe' control of feed were less rapid and effective; Ifvitf were' not for such effective' control a much greaterv factor of safety would have to-employed an'd the:

normal rate of feed consequently' would have to be cut down.

While I have illustrated and described in detailcertain preferred formsl of my` invention,vit is to be understoodV changesl may be made therein and the invention embodied -n otherstructures.

I do not, therefore; desire tolimit myself vto thev specific construction illustratedf-but-intend to Thus there is no danger of breakageor injury of theY parts due to overfeed Ver-y smooth operation and absence of vibrationresult? with attendant high quality of Workand savingof wear and tearl lill 8 cover my invention broadly in whatever form its principles may be utilized.

What is claimed is:

1. A hydraulic feed for machine tools comf prising an actuator for bringing about relative feed between the tool and the Work, a source of liquid under pressure, a pressureY line leading from the pressure source to the actuator, an accumu-v lator in said line in communication with the' acv tuator during the machining operation, and an automatic regulator in said pressure line bei tween the source of -pressure and the actuator, said automatic regulator including a valveI for controlling flow through said pressure' line, and air pressure means for actuating said valve.,

2. A hydraulic feed for machine tools comprie-f ing anactuator for bringing about relative feed between the tool and the work, a source'of liquid under pressure, a pressurel line leading from the pressure source to the actuator, an accumulator in said line in communication with the actuator during the machining operation, and an automatic regulator in said pressure line between the' accumulator and the actuator, said automatic' regulator including a valve for controlling ilow through said pressure line, and air pressure' means for actuating said valve.

3. A hydraulic feed for machine tools compris-l ing an actuator for bringing about relative feed between the tool and the work, a source of liquid' under pressure, a pressure line leading' from the pressure source to the actuator, an accumulator in said line in communication With-the actuator during the machining operation, an automatic regulator in said pressure line between the accu'- mulator" and the actuator, a returnline leadingl from the actuator, an automaticY regulatorin said' return line, and connections from the air space" of said accumulator to said return line .automatic regulator whereby the return line automatic rege ulator is governed by pressures in the air space'of said accumulator.

4. A hydraulic feed for machine tooisicomprislj ing'an actuator for bringing about'relartiv'e feed' between the tool and the worlna source of liquid' under pressure, a pressure linel leading from theA pressure source to the actuaton'an'accumulator'- including a Valve for controlling ilowthroughl said pressure line, and air pressure means for'actuat'--vv ing said valve. y v Y 5. A hydraulic feed for machine toolscomprs? ingan actuator for bringingabout'relative feedk between the tool and the'work, a source of liquid" under pressure, a pressure line leading from theV pressure source to the actuator, lan accumulatorl in said line in communication with the actuator during the machining operation, an automatic" regulator in said pressure line between the' accumulator and the actuator, a' reversing valve in said pressure line between the automatic' regu-` lator and the actuator, and a connection from' said reversing valve to' said automatic regulator"- whereby the automatic regulator is controlled byy the pressure in said actuator transmitted through said reversing valve, said automatic regulator'in'-`A cludng a valve for controllingV flowthroug'hsa'id'.' pressure line, and air pressure'means for actuat=v lingsaid-valve. Y

6". A 'hydraulic `feed*formachineto'lgcomprisi ing an actuator for bringing about relative feed between the tool and the work, a source of liquid under pressure, a pressure line leading from the pressure source to the actuator, an accumulator in said line in communication with the actuator during the machining operation, an automatic regulator in said pressure line between the accumulator and the actuator, a reversing valve in said pressure'line between the automatic regulator and the actuator, a connection from said reversing valve to said automatic regulator whereby the automatic regulator is controlled by the pressure in said actuator transmitted through said reversing valve, a return line leading from the actuator, an automaticJ regulator in said return line, and connections from the air space of said accumulator to said return line automatic regulator whereby the return line automatic regulator is governed by pressures in the air space of said accumulator.

7. A hydraulic feed for machine tools comprising an actuator for bringing about relative feed between the tool and the work, a source of liquid under pressure, a pressure line leading from the pressure source to the actuator, a return line leading from the actuator, an accumulator in one of said lines in communication with the actuator during the machining operation, an automatic regulator in the other of said lines, and connections from the air space of said accumulator to said automatic regulator whereby the action of the automatic regulator is governed by pressures in the air space of said accumulator.

8. A hydraulic feed for machine tools comprising an actuator for bringingabout relative feed between the tool and the work, a source of liquid under pressure, a pressure line leading from the pressure source to the actuator, a return line leading from the actuator, and automatic regulators in each of said lines, both of said regulators being governed by changes of pressures in the pressure line.

9. A hydraulic feed for machine tools comprising an actuator for bringing about relative feed between the tool-and the work, a source of liquid under pressure, a pressure line leading from the pressure source to the actuator, an automatic regulator in said pressure line including a throttle valve in the pressure line, and means for actuating said throttle valvweL including a pressure responsive valve actua 'ng element, a source of pressure for operating said Valve actuating element, a pilot valve for governing the flow of pressure to said valve actuating element, and

means responsive to changes of pressure in the pressure line for actuating said pilot valve.

10. A hydraulic feed for machine tools comprising an actuator for bringing about relative feed between the tool and the work, a source of liquid under pressure, a pressure line leading from the pressure source to the actuator, an automatic regulator in said pressure line including a throttle valve in the pressure line, and means` for actuating said throttle valve including a pressure responsive valve actuating element, a source of pressure for operating said valve actuating element, a pilot valve for governing the flow of pressure to said valve actuating element, means re"A 11. A hydraulic feed for machine tools comprising an actuator for bringing about relative feed between the tool and the work, a source of liquid under pressure, a pressure line leading from the pressure source to the actuator, an accumulator in said pressure line, a return line leading from the actuator, pressure regulators in said pressure line and return line respectively, each of said pressure regulators including a throttle valve and diaphragm means for actuating the same, an air pressure line for supplyingair pressure for actuating said diaphragms, each of said regulators having pilot valve means for controlling the action of the air pressure upon the diaphragm of the respective regulator, means for connecting the pilot mechanism of one of said regulators with the pressure line, and means for connecting the pilot mechanism of the other regulator with the air space at the top of said accumulator.

12. A hydraulic feed for machine tools comprising an actuator for bringing about relative feed between the tool and the work, a source of liquid under pressure, a pressure line leading from the pressure source to the actuator, an accumulator in said pressure line, a return line leading from the actuator, pressure regulators in said pressure line and return line respectively, each of said pressure regulators including a throttle valve and diaphragm means for actuating the same, an air pressure line for supplying air pressure for actuating said diaphragms, each of said regulators having pilot valve means for controlling the action of the air pressure upon the diaphragm of the respective regulator, means for connecting the pilot mechanism of one of said regulators with the pressure line, means for connecting the pilot mechanism of the other regulator with the air space at the top of said accumulator, and means responsive to movements of the actuator for cutting off the supply of air pressure from said regulators during part of the stroke of the actuator.

13. A hydraulic feed system for machine tools comprising an actuator for bringing about relative feed between the tool and the work, and a liquid supply circuit comprising, in order, a reservoir, means for supplying liquid therefrom under substantially constant pressure, a liquid supply line, an accumulator connected to the line, a throttle, a supply connection to the actuator, the actuator, a discharge connection from the actuator, a throttle and a return line`to the reservoir, the circuit being arranged so that the force applied by the actuator is controlled by the throttles and is decreased by increasing the throttling and automatic throttle control mechanism responsive to pressure at the actuator for increasing the throttling upon rise of pressure in the high pressure end of the actuator.

14. A hydraulic feed system according t0 claim 13, comprising also automatic throttle control mechanism responsive to pressure in the accumulator.

ALBERT A. ERICSON.

REFERENCE S CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,905,133 Bishop et al 'Apr. 25, 1933 1,996,466 Ernst Apr. 2, 1935 2,005,731 Ernst et al June 25, 1935 2,034,157 Stacy Mar. 17, 1936 2,272,684 Vickers Feb. 10, 1942 

